The cap is similar to that of Agaricus campestris (the field mushroom). The gills are white at first (when this fungus is most often confused with deadly Amanita genus). They later pass through grey and brown to become dull chocolate. There is a large spreading ring, white above but sometimes with yellowish scales underneath. Viewed from below, on a closed-cap specimen, the twin-layered ring has a well-developed 'cogwheel' pattern around the stipe. This is the lower part of the double ring. The odor is described as like anise.[1] It belongs to a group of Agaricus which tend to stain yellow on bruising.

It is one of the largest white Agaricus species in Britain (where it appears during the months of July-November), West Asia (Iran)[3] and North America. Frequently found near stables, as well as in meadows, it may form fairy rings. The mushroom is often found growing with nettles (a plant that also likes nutrient-rich soil). It is sometimes found associated with spruce.[4]

Much prized by farmers and gypsies for generations, the horse mushroom is regarded as one of the most delicious edible fungi, although the fruitbodies of this and other yellow-staining Agaricus species often have a build-up of heavy metals, such as cadmium and copper.[5]